This application claims priority on Japanese Patent Application No. 2000-93218, filed on Mar. 30, 2000 and Japanese Patent Application No. 2000-195113, filed on Jun. 28, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to hydraulic units, wherein torque is generated upon the relative rotation of a case and a spindle and communicated instantaneously from the case to the spindle, and to electric power tools, such as impact screwdrivers and other electric tools, to which such hydraulic units are incorporated.
2. Description of the Related Art
A typical hydraulic unit includes a working fluid-filled cylindrical case to which torque from motors and other such apparatuses is transmitted and a spindle which passes through the interior of the case, the shaft of the spindle being supported by closing elements disposed at both ends of the case. The spindle is further provided with blades or other seal bodies/structures protruding radially therefrom so as to circumferentially partition and seal the interior of the case into a plurality of fluid chambers. As the case and spindle are caused to rotate in relation to each other, certain fluid chambers are sealed by the engagement of the blades and ribs or other structures formed in the interior of the case, causing an increase in hydraulic pressure, thereby generating instantaneous torque to the spindle. However, in a hydraulic unit of this design, changes in the temperature in the working fluid result in a change in fluid volume, thus altering the output torque. Japanese Patent No. 2718500 discloses an invention wherein a partitioning wall provided in the interior of a hydraulic unit case forms a low-pressure chamber adjacent to the fluid chamber in the axial direction, and further wherein a spindle is inserted through the partitioning wall, creating very small clearance between this wall and the spindle. Disposed in the interior of the low-pressure chamber is circular piston into which the spindle is loosely inserted, and a biasing force to compress the low-pressure chamber is applied to the piston by a coil spring disposed on the other side of the partitioning wall. This arrangement allows fluctuations in the working fluid volume to be neutralized by the flow of working fluid into and out of the low-pressure chamber, thus stabilizing the output torque.
While this pressure stabilizing mechanism achieves its intended objective, it suffers from certain deficiencies that reduce its utility. In the foregoing mechanism, for example, in addition to the circular piston and coil spring, numerous parts, including the fluid chamber""s partitioning wall and seal rings, are required for the formation of the low-pressure chamber, thereby resulting in increased costs and greater size requirements for the hydraulic unit, as it is lengthened in the axial direction.
The same Japanese patent also discloses an arrangement wherein an auxiliary pressure regulating chamber disposed adjacent to the fluid chamber is stopped by a threaded adjustment screw, and further wherein the peak pressure of the fluid chamber, and therefore the maximum output torque, can be changed by making adjustments in the pressure regulating chamber""s capacity with the adjustment screw. However, according to this arrangement, the pressure regulating chamber is completely separated from the previously mentioned low-pressure chamber used for stabilizing the output torque. Therefore, provision of both of these arrangements further increases the number of parts required, which also then serves to increase costs. Furthermore, securing required space for the adjustment mechanism places additional limitations on the form of the fluid chamber and other components.
In addition, errors in the maximum output torque of the hydraulic unit as described above may occur when the hydraulic unit is incorporated in an electric power tool, the maximum output torque deviating from initial settings as a result of leakage of the working fluid during use or other causes. Such errors necessitate a laborious process of temporarily removing the hydraulic unit from the electric power tool, adjusting the adjustment screw to adjust the output torque to the proper level, and reinstalling the hydraulic unit in the electric power tool. These disadvantages have a significantly negative effect on the ease in use of the tool.
In view of the above-identified problems, an important object of the present invention is to provide a hydraulic unit wherein the output torque can be maintained at a stable level while adjustment of the maximum output torque can be performed using a simple process without involving numerous parts.
Another object of the present invention is to provide an electric power tool incorporating the above hydraulic unit that can be manufactured with greater compactness and for which the process of adjusting the maximum output torque can be carried out simply.
The above objects and other related objects are realized by the invention which provides a hydraulic unit comprising a generally cylindrical case containing working fluid, the case having an interior and front and rear closing elements at two axial ends thereof. The hydraulic unit further comprises a spindle which is inserted into the case and includes front and rear ends rotatably supported by the front and rear closing elements, respectively, the spindle further including a plurality of seal bodies for circumferentially partitioning an interior of the case into a plurality of fluid chambers whereby relative rotation between the case and the spindle causes the interior of the case and the seal bodies to seal specified fluid chambers, raising the fluid pressure in specified fluid chambers and generating instantaneous torque to the spindle. In the hydraulic unit, the rear closing element of the case is axially slidably disposed within the case and includes a closed-end hole having a bottom -surface opposing the rear end of the spindle. Moreover, the spindle further includes a fluid channeling passage formed therein for introducing part of the working fluid within the specified fluid chambers to the bottom surface of the closed-end hole, and the hydraulic unit further comprises an elastic member for biasing the rear closing element toward the fluid chambers and an adjustment member for adjusting the biasing force of the elastic member. In the above hydraulic unit, the peak pressure can be maintained and the output torque stabilized at a desired level, even when there is a change in pressure within the fluid chambers resulting from an increase in the temperature of the working fluid. Additionally, the hydraulic unit provides a simplified process for adjustment of its maximum output torque, which can be realized by rotation of the adjustment member that in turn changes the biasing force of the elastic member. In particular, by using the closed-end hole supporting the rear end of the spindle as the portion for accommodating pressure changes while employing the elastic member for both the adjustment and stabilization of output torque, this construction provides a practical arrangement that requires little additional space and permits a reduction in the number of parts used. This both enhances compactness and allows suppression of additional costs.
According to one aspect of the present invention, the elastic member comprises a disk spring disposed at the rear of the rear closing member, and the adjustment member comprises a nut member disposed at the rear of the disk spring and threadably engaged to the case. This feature advantageously reduces the space required in the axial direction and greatly enhancing the compactness of the hydraulic unit.
According to another aspect of the present invention, the case has internal threads on an rear internal surface thereof, and the nut member has external threads so as to engage the internal threads of the case and axially slide relative to the case when rotated, thereby permitting adjustment of the axial position of the nut member and thus the biasing force of the disk spring.
According to still another aspect of the present invention, the rear closing element is a stepped circular member having a large-diameter section in which the closed-end hole is formed and having a reduced-diameter section extending rearward from the large-diameter section. The reduced-diameter section has an inner circular surface and an outer circular surface around which the nut member is axially slidably fitted.
According to yet another aspect of the present invention, the inner surface of the reduced-diameter section defines a second closed-end hole adapted to receive an output shaft coupled to a motor for receiving torque of the motor.
In one feature of the present invention, the rear closing element is slidable between a front position, attained when the fluid pressure in the specified fluid chambers is lower than a threshold, and a rear position, attained when the fluid pressure in the specified fluid chambers reaches or exceeds the threshold. When the rear closing element is in the front position, the large-diameter section abuts rear ends of the seal bodies. Conversely, when the rear closing element is in the rear position, the large-diameter section is detached from the rear ends of the seal bodies as a result of introduction of the working fluid into the closed-end hole via the fluid channeling passage.
In another feature of the present invention, the fluid channeling passage includes a through-hole axially formed through the rear end of the spindle to the closed-end hole and at least one axial communicating hole formed in the spindle. The communicating hole is adapted to be in communication with the fluid chambers at one end thereof and with the through-hole at another end thereof, such that the communicating hole introduces the working fluid into the through-hole when the seal bodies of the spindle are tilted relative to the case during generation of a hydraulic impulse by the hydraulic unit, thus permitting introduction of the working fluid into the closed-end hole when the fluid pressure in the fluid chambers reaches or exceeds the threshold.
In still another feature of the present invention, the threshold corresponds to the biasing force of the disk spring and is selected by adjustment of the disk spring""s biasing force.
The invention is further directed to an electric power tool having a housing, a motor, a hydraulic unit as defined above encased in the housing, and an output shaft of the motor for transmitting rotation of the motor to hydraulic unit""s spindle via the hydraulic unit""s case.
The present invention provides for an electric power tool having a motor, a housing, a hydraulic unit as defined above encased in the housing, and a first spindle for transmitting rotation of the motor to hydraulic unit""s spindle via the hydraulic unit""s case. The electric power tool includes an adjustment mechanism for preventing rotation of the case in cooperation with an adjusting tool inserted into the electric power tool through the housing while simultaneously permitting operation of the hydraulic unit""s adjustment member to adjust the biasing force of the elastic member in cooperation with the adjusting tool. This permits simplified adjustment of the hydraulic unit""s maximum torque by insertion of an adjustment tool, eliminating the need to completely remove the hydraulic unit from the housing, make the necessary adjustments, then reassemble the apparatus, thereby affording better adjustment operability and greater convenience in the use of the electric power tool.
In one aspect, the adjustment mechanism includes a plurality of meshing cogs formed on an axial end surface of the nut member and disposed about a circle described about the axis of the nut member, with the meshing cogs being adapted to engage and be rotated by the adjusting tool. The adjustment mechanism additionally includes an insertion hole extending radially along the nut member""s end surface from the meshing cogs to an opening formed on an exterior surface of the housing. Further included in the adjustment mechanism is at least one rotation stop section located between the insertion hole and the meshing cogs. The rotation stop section prevents rotation of the case by interfering with the adjusting tool when the adjusting tool is inserted into the insertion hole to engage the meshing cogs.
In another aspect, the nut member includes a nut and a ring disposed at the rear of the nut. The nut has an axial front end surface on which the disk-spring is disposed, whereas the ring is securely connected to the nut so as to integrally rotatable with the nut and having an axial rear end surface on which the meshing cogs are formed.
In a further aspect, the electric power tool further includes a coupling which is connected to the first spindle and disposed between the first spindle and the case of the hydraulic unit for transmitting the torque of the first spindle to the case. The coupling includes, as the at least one rotation stop sections, a plurality of radially extending semicircular grooves formed therein.
In another aspect of the invention, four radially extending semicircular grooves are arranged at regular intervals in an axial front end surface of the coupling where they oppose the meshing cogs.